arXiv subjects

Łukasz G. Gajewski

Publications and source records attributed to Łukasz G. Gajewski.

7 recordsLinked to original sources

arXiv2025

Quantitative, Data-driven Network Model for Global Cascading Financial Failure

Global catastrophic risk events, such as nuclear war, pose a severe threat to the stability of international financial systems. As evidenced by even less severe scenarios like the Great Recession, an economic failure can propagate through the world trade network, wreaking havoc on the global economy. While the contemporary literature on cascading failure models addresses this issue qualitatively, a simple and intuitive quantitative estimation that could be used in integrated assessment frameworks is missing. In this study, we introduce a quantitative network model of global financial cascading failure. Our proposal is a fast, efficient, single free parameter model, following a straightforward logic of propagating failures. We fit the model to the Great Recession and test it against historical examples and commercial analysis. We also provide predictions for a hypothetical armed conflict between India and Pakistan. Our aim is to introduce a quantitative approach that could inform policy decisions by contextualising global catastrophic scenarios regarding financial losses and assessing the effectiveness of resilience strategies, complementing existing models and frameworks for broader risk assessment.

physics.soc-ph↗

arXiv2024

Global transformer overheating from geomagnetic storms

Geomagnetic storms occurring due to sustained, high-speed solar winds are known to induce currents in power distribution networks. These geomagnetically induced currents (GICs) can cause high voltage transformers (HVT) to overheat, thus resulting in a catastrophic electricity loss event (CELE). Since significant portions of infrastructures around the world rely heavily on access to electric power, it is essential to estimate the risks associated with GICs on a global scale. We assemble multiple methodologies across various scientific disciplines to develop a framework assessing the probability of a severe geomagnetic storm causing a long-term, widespread power outage. Our model incorporates thermal models of HVT tie bar hot spots, historical geoelectric field estimates, and a global conductivity model to estimate the risk of long-term power outage for regions between -70 degrees and 80 degrees geomagnetic latitude due to transformer overheating failure. Assuming a uniform 33% HVT spare capacity, our analysis indicates that a 1 in 10,000 year storm would result in approximately 1% of the population in Europe and North America experiencing a long-term (months to years) electricity loss.

physics.soc-ph↗

arXiv2022

Transitions between polarization and radicalization in a temporal bilayer echo chambers model

Echo chambers and polarisation dynamics are as of late a very prominent topic in scientific communities around the world. As these phenomena directly affect our lives and seemingly more and more as our societies and communication channels evolve it becomes ever so important for us to understand the intricacies of opinion dynamics in the modern era. Here we extend an existing echo chambers model with activity driven agents onto a bi-layer topology and study the dynamics of the polarised state as a function of interlayer couplings. Different cases of such couplings are presented - unidirectional coupling that can be reduced to a mono-layer facing an external bias, symmetric and non-symmetric couplings. We have assumed that initial conditions impose system polarisation and agent opinions are different for both layers. Such a pre-conditioned polarised state can sustain without explicit homophilic interactions provided the coupling strength between agents belonging to different layers is weak enough. For a strong unidirectional or attractive coupling between two layers a discontinuous transition to a radicalised state takes place when mean opinions in both layers are the same. When coupling constants between the layers are of different signs the system exhibits sustained or decaying oscillations. Transitions between these states are analysed using a mean field approximation and classified in the framework of bifurcation theory.

physics.soc-ph↗

arXiv2021

Discovering hidden layers in quantum graphs

Finding hidden layers in complex networks is an important and a non-trivial problem in modern science. We explore the framework of quantum graphs to determine whether concealed parts of a multi-layer system exist and if so then what is their extent, i.e., how many unknown layers there are. Assuming that all information available is the time evolution of a wave propagation on a single layer of a network it is indeed possible to uncover that which is hidden by merely observing the dynamics. We present evidence on both synthetic and real-world networks that the frequency spectrum of the wave dynamics can express distinct features in the form of additional frequency peaks. These peaks exhibit dependence on the number of layers taking part in the propagation and thus allowing for the extraction of said number. We show that in fact, with sufficient observation time, one can fully reconstruct the row-normalised adjacency matrix spectrum. We compare our propositions to a machine learning approach using a modified, for the purposes of multi-layer systems, wave packet signature method.

cond-mat.dis-nn↗

arXiv2021

Detecting Hidden Layers from Spreading Dynamics on Complex Networks

When dealing with spreading processes on networks it can be of the utmost importance to test the reliability of data and identify potential unobserved spreading paths. In this paper we address these problems and propose methods for hidden layer identification and reconstruction. We also explore the interplay between difficulty of the task and the structure of the multilayer network describing the whole system where the spreading process occurs. Our methods stem from an exact expression for the likelihood of a cascade in the Susceptible-Infected model on an arbitrary graph. We then show that by imploring statistical properties of unimodal distributions and simple heuristics describing joint likelihood of a series of cascades one can obtain an estimate of both existence of a hidden layer and its content with success rates far exceeding those of a null model. We conduct our analyses on both synthetic and real-world networks providing evidence for the viability of the approach presented.

physics.soc-ph↗

arXiv2020

Source location on multilayer networks

Nowadays it is not uncommon to have to deal with dissemination on multi-layered networks and often finding the source of said propagation can be a crucial task. In this paper we tackle this exact problem with a maximum likelihood approach that we extend to be operational on multi-layered graphs. We test our method for source location estimation on synthetic networks and outline its potential strengths and limitations. We also observe some non-trivial and perhaps surprising phenomena where the more of the system one observes the worse the results become whereas increased problem complexity in the form of more layers can actually improve our performance.

cs.SI↗

arXiv2020

Optimizing sensors placement in complex networks for localization of hidden signal source: A review

As the world becomes more and more interconnected, our everyday objects become part of the Internet of Things, and our lives get more and more mirrored in virtual reality, where every piece of~information, including misinformation, fake news and malware, can spread very fast practically anonymously. To suppress such uncontrolled spread, efficient computer systems and algorithms capable to~track down such malicious information spread have to be developed. Currently, the most effective methods for source localization are based on sensors which provide the times at which they detect the~spread. We investigate the problem of the optimal placement of such sensors in complex networks and propose a new graph measure, called Collective Betweenness, which we compare against four other metrics. Extensive numerical tests are performed on different types of complex networks over the wide ranges of densities of sensors and stochasticities of signal. In these tests, we discovered clear difference in comparative performance of the investigated optimal placement methods between real or scale-free synthetic networks versus narrow degree distribution networks. The former have a clear region for any given method's dominance in contrast to the latter where the performance maps are less homogeneous. We find that while choosing the best method is very network and spread dependent, there are two methods that consistently stand out. High Variance Observers seem to do very well for spread with low stochasticity whereas Collective Betwenness, introduced in this paper, thrives when the spread is highly unpredictable.

cs.SI↗